Although orthostatic hypotension (a condition whereby systolic blood pressure drops with change in posture) has been studied at length, orthostatic hypertension is a phenomenon that is not yet fully understood by medical researchers. It appears to be triggered by the sympathetic nervous system and is manifested in a variety of illnesses.
Identification
The definition of orthostatic hypertension is an increase of 20 mmHg (millimeters of mercury, the units in which blood pressure is measured) for each change in posture from lying down, to sitting upright, to fully standing. The aspect of pressure being measured is systolic pressure, which is the maximum pressure exerted on the arteries from the left lower chamber of the heart that occurs when the heart is contracting. It is the top number when the health care provider tells a patient his blood pressure. Normal range for this number is 110 to 120 mmHg.
Causes
Although the exact cause of orthostatic hypertention is under dispute, there are several respected hypotheses circulating. One thought is that when a person stands up, blood collects in the lower extremities and lowers the cardiac output (the amount of blood pumped by the heart in one minute). In response, the sympathetic nervous system takes over and constricts the arteries, thereby increasing pressure. For diabetic patients, it is thought that there may be a hypersensitivity of the baroreflex, which errs on the side of elevating pressure. The baroreflex is an area of the heart that relays information to the brain and influences and the sympathetic nervous system in general.
Significance
Orthostatic hypertension has been identified as a symptom of pheochromocytoma (a type of endocrine tumor). In this condition, orthostatic pressure may be elevated (hypertension) or decreased (hypotension). Orthostatic hypertension can also be detected in certain cases of POTS (postural orthostatic tachycardia syndrome). In POTS, the heart speeds its beats per minute to compensate for fluctuations in the gravitational pull of postural changes. Neuropathy (chronic numbness, pain or weakness due to nerve damage) has been associated with orthostatic hypertension in diabetic patients. According to a study by the Shimada Laboratory in Japan, incidence of silent stroke and TIAs (transient ischemic attacks, or mini-strokes) in elderly Japanese patients with a history of essential hypertension has a notable link to postural orthostatic hypertension. Of the 241 participants of the study, 11 percent displayed this feature.
Management
Management regimens tend to follow standard hypertension treatment, meaning the goal is to lower blood pressure. However, the medications selected to combat orthostatic hypertension are those that focus on inhibiting the sympathetic . The medication prazosin has proven helpful. Prazosin works by blocking the receptors that a constricting agent like norepinephrine would claim' as a result, the smooth muscle of the blood vessel is relaxed and pressure reduced. The medication clonidine has also proven successful in treating orthostatic hypertension. Clonidine, also known as Catapress, stimulates certain receptors in the brain, which in turn lowers cardiac output and vascular muscle tone. It also decreases the level of calcium and norepinephrine in the bloodstream, which further lowers blood pressure.
Expert Insight
It is important to note that a study by Kario, et al. established that a correlation exists between orthostatic hypertension and cardiovascular disease in the elderly. The study, conducted in 2002, comprised orthostatic hypertensives, orthostatic hypotensives and those with normal orthostatic pressures. Silent strokes (stroke without symptoms) occurred three times more frequently in the group with orthostatic hypertension than in the control group (people with normal blood pressures). The study further confirmed that administering medications that affect the sympathetic response (prazosin, clonidine) fully controlled the condition. In addition to rigorous blood pressure monitoring, MRIs (magnetic resonance imaging) were utilized in the study to confirm vascular changes in the brain.
Tags: blood pressure, orthostatic hypertension, nervous system, sympathetic nervous, sympathetic nervous system, cardiac output